(a) Field of the invention
The present invention relates to a non-invasive method for a full three-dimensional dynamic free motion analysis of the trunk, spine, pelvis and intersegmental movement of a patient.
More particularly, the invention relates to a non-invasive method for the dynamic evaluation of the flexibility of the spine of a patient and, as a result of this evaluation, the detection and identification of possible mechanical injuries in some portion of this spine, especially the lumbar portion thereof.
The invention also relates to an equipment for carrying out this method.
(b) Brief description of the prior art
It is well known in the medical art that common back disorders have a mechanical etiology. It is also well known from pathological studies that there are two common patterns of disc injury which correspond to two different types of mechanical failure of the spine.
The first type of common injury hereinafter referred to as "compression injury", usually starts by a central damage to the disk with fracture o varying magnitude of the end plates of the adjacent vertebrae, sometimes followed by injection of part of the nucleus into the vertebral body. In this particular case, the injured end plate permits the invasion of the avascular nucleus and of the avascular inner portion of the annulus by granulation tissue ingrowing through the fractured end plate, such an invasion leading to gradual destruction of the avascular nucleus and inner annulus. In the early stages, the facet joints of the vertebrae are not affected and the outer annulus survives while the center portion of the disc is destroyed. With progression, the disc loses its thickness while the outer layer of the annulus remains relatively well preserved. With lost of disk thickness, the facet joint subluxates and develops a moderate degree of osteoarthritis.
Usually, the fracture of the end plate of a vertebra is an undisplaced fracture of cancellous bone which heals rapidly. The symptoms are short lived, typically lasting two weeks. The facet joint arthritis appears late. At this stage, symptoms may also arise from the reduction in size of the spinal canal (lateral or central spinal stenosis).
The other type of common injury hereinafter referred to as "torsional injury", is characterized by a damage to the annulus occurring simultaneously with a damage to the facet joints. The annulus is avulsed from the end plate and its laminae become separated while the central disk and the end plate remain intact. At the later stage, the annulus develops radial fissures while the nucleus remains relatively untouched. The changes in the facet joints are severed with massive joint destruction and osteophytosis similar to hypertropic arthritis. Relatively late in the process, there may be changes in the end-plates and central disks, with consequent collapse of the articular surfaces and chronic synovitis.
In this particular case, the basis injury is to collageneous ligamentous tissue which requires six weeks to regain 60% of its strength. Because the injury involves both the disk and facet joints, it is more difficult for the joint to stabilize itself and recurrence is frequent. The condition is progressive and may lead to spinal stenosis, instability and degenerative spondilolisthesis.
Tests conducted in laboratory have shown that a compression injury is easily produced by compressing a joint between 2 Mpa to 6 Mpa. A torsional injury can be seen with as little as 2 to 3 degrees of forced rotation requiring only 22 to 33 Newton-meters of torque.
Statistically, in a group of patients suffering from back disorders, 64% exhibit torsional injuries whereas 35% exhibit axial compression injuries. Statistics have also shown that torsional injury occurs mainly at the L.sub.4 -L.sub.5 level (almost 76% of forth joint problems are of torsional nature). Statistics have also shown that almost 98% of the compression injuries occur at the L.sub.5 -S.sub.1 level. Statistics have further shown that double injuries where the joint is injured both in compression and torsion, occur in 22% of the cases, invariably at the L.sub.5 -S.sub.1 level.
The following Table I reflects the probabilities of injuries among patients complaining from backache and sciatica, or sciatica alone. As can be seen from this Table, the important frequency of torsional injury cannot be overlooked. As can also be seen, the probability of a third type of injury giving symptoms is very remote.
TABLE I ______________________________________ CLINICAL DETERMINATION OF THE VARIOUS PROBABILITIES OF INJURIES JOINT P (injury) P (compression) P (torsion) ______________________________________ L.sub.5 /S.sub.1 47% 98% 22% L.sub.4 /L.sub.5 47% 1%&lt; 76% L.sub.3 /L.sub.4 5%&lt; 1%&lt; 1%&lt; L.sub.2 /L.sub.3 1%&lt; 1%&lt; 1%&lt; L.sub.1 /L.sub.2 1%&lt; 1%&lt; 1%&lt; 100% 100% 100% ______________________________________
It is also well known that health professionals are trained to use symptoms in the determination of diagnoses, the large numbers of known symptoms being quite naturally associated with a large number injuries and diagnoses. Unfortunately, as can be understood from the above short description of the pathology in the case of back disorders, both the compression and torsion injuries may give rise to identical symptomology. Hence, symptoms cannot be used to diagnose a type of injury because identical symptoms may arise from different injuries.
It is also well known in the art that low back pain is the leading cause of disability in North America today, affecting from 8 to 9 million people. It is the most common disability in persons under the age of 45 and the third only after arthritis and heart disease in those over have a low back pain at some time of their lives, usually between the ages of 20 and 50. The fact that problems are so common in people of working age is not coincidental. Indeed, most of the back problems are work-related. As the injury caused by a certain task cannot be identified from the patient's symptoms, it is of course not possible to relate directly a given task to an injury mode, although such a relationship is central to the definition of tasks that will not injure a specific worker.
The economic effects of back pain and injuries are staggering. Back problems are second only to the common cold as a cause of absenteeism in the industry. It is moreover responsible for 93 million lost workdays every year and is a leading cause of reduced work capacity. Hence, an incentive for prevention of back injury is very large.
In order to unequivocally relate a given task to a given injury in the absence of any measurement of the effect of the task on a given joint, it has already been suggested to use mathematical and/or biomechanical models of spine, like the one suggested by J.M. Morris et al in their article "The Role of trunk in stability of the spine", J. Bone and Joint Surg., 43A, 1961. However, a major problem with the known models of spine, including the widely used model of J.M. Morris et al, is that they do not truly reflect the physiological behavior of the spine over the full range of capacity.
Thus, by way of example, the model of J.M. Morris et al assumes, as fundamental hypothesis, that the moment generated by the body weight and any external load carried by the patient is balanced by the combined action of the erectores spinae and the intra-abdominal pressure. This is a very poor representation of physiological behavior which is not supported by observations. Indeed, such a model predicts a total failure of the mechanism at about one fourth of the known potential of a spinal healthy spine.
The major reason why all of the models known to the inventor are defective is essentially because they give an incomplete representation of the actual anatomy of a human being. It is true that a moment-supporting member is required in such a model but this cannot be the abdominal pressure only, as suggested by J.M. Morris et al.
This established fact combined with different other anatomical observations reported in the literature, has led the inventor to devise a new mathematical representation of the anatomy of the human spine including (1) the posterior ligamentous system which has indeed the strength to support any moment generated onto the spine by the body weight and any external load carried by the patient, and (2) the extensors of the hip which have the bulk and the lever arm necessary to supply all the moment requirements to flex the spine.
In greater details, the inventor has been noted that, under normal circumstance, the motion of an individual flexing forward from zero upright down to full flexion is due to a combination of pelvis rotation and spine motion.
In the range of 0.degree. to about 45.degree. (for an unloaded spine), the posterior midline ligament system is generally inactive and, in its place, the erectores spinae and/or the abdominal muscles support most of the moment due to the body weight. From about 45.degree. to full flexion, this moment can be also supported by the midline ligament system without muscular activity. This relaxation phenomenon from muscular to ligamentous support was already noted in the art by W. F. Floyd et al in their article "The Function of the Erector Spinae Muscles in certain Movements and Postures in Man", J. Physiology, volume 129, pp. 184-203, 1955.
Using electromyographis (EMG) measurements, W. F. Floyd et al clearly saw a relation between the moment to be supported and the angle of forward flexion, and realized the meticulous coordination of muscle, ligament and joint movement. They hypothesized that in the case of injury to an intervertebral joint, this delicate coordination will be upset and this would be reflected in change of the E.M.G. pattern. Then, they embarcated on an E.M.G. study and tried to compare statistically the E.M.G. pattern of normal individuals to that of those with common back problems in the performance of a standardized simple weight lifting task. However, they gave up after testing 140 cases because the results were inconsistent.
The mathematical model devised by the inventor, takes it for granted that the pelvis acts as a "supporting base" for the entire spine, and assumes as fundamental hypothesis, that any healthy person will perform a task in such a way as to minimize and equalize the stress at each invertebral joint.
In this model, the main power for a lift is assumed to be generated by the extensors of the hip, such as the Gluteus Maximae.
The moment generated by these muscles is transmitted to the upper extremities by the trunk musculature and the posterior ligamentous system (PLS) which, for the purpose of this discussion, is composed of the midline ligament and the lumbodorsal fascia. Regardless of the inclination of the trunk, the moment generated by the extensors of the hip must equal the sum of the moment generated by the trunk musculature and PLS. Therefore, for any given hip extensor moment, one can find an infinite number of combinations to distribute this moment between trunk muscles and the PLS.
Because of the reserve capacity in performing a small weight lift, a normal individual may select a combination of ligaments and muscles which is not optimum from a stress minimization and equalization point of view. However, the reserve is reduced in the presence of injury. The option of selecting a non-optimum strategy is also reduced.
Assuming that the distribution of moment between ligaments and muscles is controlled by the requirement that stress be minimized and equalized at all lumbar joints, stress at one intervertebral joint will be defined as the ratio of the resultant compressive force acting perpendicular to the bisector of the disk to the area of the disk. In general, when muscles are used, the stress is higher than when either ligament systems are used, because the lever arms of the ligament systems are longer than those of any of the muscles. The midline ligament system can be activated only when the spine is sufficiently flexed. The hip/shoulder angle at which this ligament takes up tension is called .alpha..sub.o, which is about 45 degrees for no load. This ligament system is strong enough to support the heaviest lift and hence, when this ligament system is activated, the spinal musculature is no longer required and therefore the muscles are electrically silent. As aforesaid, this is the muscle relaxation phenomenon observed by W. F. Floyd et al.
The thoracodorsal fascia can be activated by the contractions of the abdominal muscles, in particular the internal oblique and T. abdoinis, which exert a pull at its lateral margin only when the abdominal pressure is at sufficient value to maintain a rounded abdominal cavity. This ligament system can therefore be activated for any angle of flexion. This is an essential difference when compared to the midline ligament.
Based on this new mathematical model, the present inventor has devised and patented a new method and equipment for the detection of mechanical injuries in the lumbar spine of the patient and the identification of these injuries.
According to this method which forms the subject matter of Canadian Patent No. 1,220,273 and U.S. Pat. No. 4,655,227 both assigned to DIAGNOSPINE RESEARCH INC., the electromyographic (EMG) activities of the erectores and abdominals of the patient are measured in the bilateral and symmetrical manner with respect to the spine of the patient while the same is flexing forward in the median plane and pulling up a small load. The angle of flexion .alpha. of the patient is measured during this flexion and is supplied as variable input to the mathematical model. A computer is used to run the model with its variable input in order to calculate the EMG activities of the erectores and abdominals that would normally be used by a healthy person to produce the same task. The so calculated EMG activities are then compared to the EMG activities actually measured on the patient and the parameters of the models are tuned to fit the calculated EMG activities for those measured on the patient. The amount and type of tuning that are necessary to complete the last step, are sufficient in practice to detect and identify the mechanical injuries that may be present in the lumbar spine of the patient.
Based on the same mathematical model, the present inventor has also devised and patented another method and an equipment for the detection of a mechanical abnormality or injury in the lumbar spine of a patient and for the identification of this abnormality or injury as being of the compression or torsion type.
According to this other method which forms the subject matter of Canadian patent no. 1,220,272 and U.S. Pat. No. 4,664,130 both assigned to DIAGNOSPINE RESEARCH INC., any variation of the lumbar curve of the patient is measured using a combined visual and an electromyographic (EMG) technique, and any discrepancy or asymmetry is detected in said measured variation of lumbar curve. In practice, the absence of any variation or the detection of any discrepancy or asymmetry in the case where a variation is measured, is indicative of the presence of a mechanical abnormality or injury of the lumbar spine of the patient,
In greater details, the method forming the subject matter of Canadian patent no. 1,220,272 and its U.S. counterpart U.S. Pat. No. 4,664,130, comprises the following steps.
First of all, a first pair of surface-electrodes is fixed onto the back of the patient in a bilateral and symmetrical manner with respect to his spine in the lumbar zone, in order to record the electromyographic (EMG) activities of erectores of this patient. A second pair of surface-electrodes is fixed in a bilateral manner onto the triangles of Petit of the patient in order to record the EMG activity of his Internal Oblique and a third pair of surface-electrodes is fixed in a bilateral manner behind the thighs of the patient in order to record the EMG activity of his hip extensors.
Then, the muscle activity of the patient is measured with all of the surface-electrodes while he is flexing forward in the median plane and pulling up a small load, and the EMG activities measured by each of the surface electrodes are independently recorded as a function of time. Simultaneously, the angle of flexion .alpha. of the patient is measured and recorded as a function of time. This angle .alpha. is defined as the dihedral angle between a plane passing through the hips and shoulders of the patient and a vertical plane parallel to the frontal plane of this patient.
Last of all, the recorded EMG activities that are so measured on the patient are processed to calculate the relative variations in activities of the erectores versus the hip extensors (E/H ratio) and of the Internal Oblique versus the hip extensors (A/H ratio) and plotting said E/H and A/H ratios versus .alpha., and to calculate the amount of asymmetry "a" between the recorded EMG activities measured on the right side of the patient and the recorded EMG activities measured on the left side of this patient.
The observation of a high A/H ratio which corresponds to an extensive use of the abdominals, with the simultaneous observation of a significant delay in the detection of a sharp variation of the E/H ratio at a given angle .alpha..sub.o or of no variation at all of said E/H ratio when the patient is pulling up the small load, indicate that the patient cannot relax his erectores at the beginning of the lift, such a refusal indicating in turn that the patient has difficulty to flex his spine and therefore has a joint injury of the compression or torsional type.
On the other hand, the observation of a significant variation of "a" when .alpha. varies, that is during the lift of the small lead, indicates that the joint injury in the lumbar spine is of the torsional type.
In addition to the above mentioned methods, the present inventor has devised and patented a further method and equipment for the detection of torsional injuries the lumbar spine of the patient, which method and equipment are much simpler than any others.
This method which forms the subject matter of Canadian patent no. 1,219,673 and U.S. Pat. No. 4,699,156 both assigned to DIAGNOSPINE RESEARCH INC., derives from an observation made by the inventor that a healthy spine is characterized by its ability to flex smoothly in any plane. Hence, an injury to any joint of the spine will always result in a reduced flexing range of motion of the spine.
According to this method, a string of separate, dot-sized skin-markers that may consist of small LEDs fired under computer control, are fixed onto the skin of the back of the patient in the midline of his spine from at least thoracic vertebra T.sub.10 down to at least sacral vertebra S.sub.3. A visualization equipment including two cameras spaced apart from each other, is used to observe, monitor and record the relative positions of the skin-markers on the back of the patient as he leans to the left and then to the right off his sagittal plane. The recorded positions of the skin-markers when the patient was leant to the left, are then compared with their recorded positions when the patient was leant to the right in order to determine whether there is a significant difference between both of these recorded positions, and in the case where there is such a significant difference, whether these different recorded positions are symmetrical with respect to the sagittal plane.
In practice, the observation of a non-significant difference between the recorded positions of the skin-markers indicates a refusal by the patient to flex his spine, such a refusal in turn indicating the presence of a double torsional injury having damaged any lumbar intervertebral joints statistically between vertebrae L.sub.4 and L.sub.5 or L.sub.5 and S.sub.1. On the other hand, provided that the recorded positions of the skin-markers are different, the observation of a substantial asymmetry between the recorded positions indicates a refusal by the patient to flex his spine in one direction, such a refusal in turn indicating the presence of a simple torsional injury at any lumbar intervertebral joints statistically between vertebrae L.sub.4 and L.sub.5 or L.sub.5 and S.sub.1.
The latter method and the very particular equipment used for carrying it out, have been actually reduced into practice and successfully tested. In addition to being a real and true scientific diagnosis tool, this method as well as all the other methods devised by the present inventor and mentioned therein above, have the major advantage of being of the "non-invasive" type, essentially because they do not require "invasive" tools such as X-rays, needles and the like to collect the physiological data necessary for detecting the presence of a mechanical abnormality or injury.
It is worth mentioning that other non-invasive methods are known and presently used for evaluating the musculature involved in truck flexion and extension and/or the flexibility of a patient's back.
By way of example, U.S. Pat. No. 4,600,012 issued on July 15, 1986 to CANON KABUSHIKI KAISHA discloses a method and an apparatus for detecting abnormality in the spine of a patient. According to this method which is based on the presumption that an abnormality in the positions of the shoulders is indicative of an abnormality in the spine, light lines are projected parallel to the spine on the right and left sides of the back of the patient and monitored to determine the positions of the shoulders of this patient while the same is bending forward. The observation of a difference in the heights of the left and right shoulders in the forward bent posture, is allegedly indicative of a spinal abnormality such as a lateral spinal curvature.
The major problem with this method is that there are cases where the shoulder positions may "look" abnormal while the spine is normal and other cases where the shoulder positions look normal but the spine is seriously damaged (by way of example, a compression injury with an end plate fracture will result in the injection of the nucleus in the vertebrae body but will not prevent the patient from getting a symmetrical motion during forward flexion).
French laid-open patent application no. 2,449,433 to Jean MAURER discloses a method and equipment for visualizing spine deformation. According to this method, an adhesive band having a flexibility and elasticity compatible with the body motion in the spinal zone is "glued" onto the skin of the patient's back to follow the axis of his spine. The band supports a helicoidal bellows of flexible material which incorporates a plurality of goniometers for recording and transmitting data indicative of their respective positions and orientations preferably via a cable, to a T.V. monitor. The image displayed on the screen is divided into two parts in which are respectively shown the recorded position of the spine in the sagittal plane of the patient (antero-posterior bends) and the recorded position of the spine in the frontal plane (lateral bends). Reference lines may also be displayed to allow the patient to visualize the difference between a "normal" spine and his spine.
A first problem encountered in the MAUGER's method is that the goniometers used as "sensors" may only give 2-dimensional signals. This is unfortunately a substantial source of error as the coupling motion of a spine is much more complex, 1% of lateral bent of one joint frequently inducing up to 0.66% of simultaneous axial rotation.
Another problem in MAUGER is that the adhesive band used to fix the goniometers must be wide enough to support the bellows and sensors. Because of this width, the band extends on both sides of the epiphysis of each vertebra, along which a very active muscle called multifidus extends. Of course, this muscle "moves" on its own when 10 the spine moves and affects the orientation of the goniometers fixed to the band. Thus, if the patient while he is performing an exercise, has for any reason a muscular spasm, this motion will be sensed by the adjacent goniometer as a spinal motion and will create another very substantial error in the displayed data.
The same problem is obviously encountered in the equipment presently sold by the U.S. Company MOTION ANALYSIS CORPORATION of SANTA ROSA, California, under the trade name SPINETRAK. This equipment which is intended to be used for measuring and evaluating "the range of motion of the cervical, thoracic and lumbar spine, the spine kinematics with velocity and acceleration in three movement modes and the total thoraco-lumbar, lumbo-pelvic and femoral-pelvic motion", makes use of strings of skin-markers that are fixed laterally and symmetrically on both sides of the spine, on top of the shoulders and along the hips, or on both sides of the neck, on top of the shoulders and around the skull and whose respective positions are tracked, plotted and processed to evaluate the flexibility of the lumbar or cervical portion of the spine. Once again, most the sensors"(i.e. the skin-markers) used in this equipment, including in particular those used to track the lumbar portion of the spine, are fixed onto muscles that move on their own when the spine moves and thus create errors in the resulting data.
Another equipment is presently offered for sale by the U.S. Company LOREDAN BIOMEDICAL of DAVIS, California, under the trade name LIDO.RTM. Back Isokinetic System, to evaluate and rehabilitate the musculature involved in trunk flexion and extension. In this equipment, the patent's pelvis is rigidly strapped and his chest attached to a sliding chest carriage that constrains the trunk to rotate about a single axis. Thus, the patient performs difference isokinetic exercises in either sitting or standing position. During these exercises, the patient's torque and the angular velocity of his movement are measured and used to evaluate his physical condition.
A major limitation of this equipment is that it evaluates the spine function while the patient trunk is allowed to rotate about a single axis while the human spine actually has 24 mobile vertebrae, i.e. 24 centers of rotation, that are also rotate over a moving pelvis.